Purification of titanium by washing and froth flotation



United States Patent PURIFICATION OF TKTANIUM BY WASHING AND FROTH FLOTATION Merle E. Sibert, Garfield Heights, Ohio, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy No Drawing. Application April 25, 1951, Serial No. 222,937

1 Claim. (Cl. 75121) If titanium contains even very small amounts of foreign materials from the primary stages of reduction to metal, it lacks ductility and necessary workability. Inclusion of such materials can be avoided by a suitable procedure and precautions. For instance, by the process in the application of M. A. Steinberg, M. E. Sibert and A. A. Topinka, Serial No. 202,806, it is possible to produce titanium electrolytically to desired standard of purity. However, where foreign materials have not been avoided it is still possible by the features of the present invention to prepare the metal to proper standards. Thus, titanium carrying materials such as oxide, carbide, and salts by its initial formation can be brought to finished condition providing properly ductile metal. Other objects and advantages of the invention will appear from the following description.

To the accomplishment of the foregoing and related ends, said invention then comprises the features hereinafter fully described and particularly pointed out in the claim, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

in such electrolytic preparation of titanium in an alkaline earth chloride fused bath, for example, the titanium deposits on the cathode in the form of a black spongy mass, admixed with impurities such as alkaline earth halide from the electrolytic bath, other calcium compounds, including calcium carbide, carbon if graphite be present in the cell, titanium carbide, and titanium monoxide. Carbon in combined or free form, and oxides, are especially detrimental, as titanium metal is peculiar in that very small amounts of carbon and oxygen render the metal so hard and brittle that it cannot be mechanically worked. In the present process, the titanium metal is prepared in a manner to be freed from such detrimental materials and be formed as a finished product which is ductile. If titanium metal powder be fused in the presence of carbon or oxygen or both, these latter elements go into solid solution in titanium and no method is known for mechanical separation after such fuslon has taken place. X-ray defraction examination shows that in electrolytically formed titanium according to the present invention, carbon and oxygen, if present, are separate entities, and these can be removed mechanically in op erations leading up to the ultimate fusion and formation of ductile metal.

In a typical case, the titanium develops in the primary stage of reduction as a loose black spongy mass. ThlS I give a primary wash in warm water at a temperature of about 60 C. to remove most of the free calcium chloride. When wetted, some areas of the deposit appear black and others grey. These black areas are heavy in titanium carbide and generally the extreme upper and lower tenths of the material exhibit this character. These carbided areas preferably are sliced or sawed oil? and treated separately from the major relative pure portions.

The material is next dispersed in about 20 times its volume of pure water and heated to the boiling point for 30 to 60 minutes with vigorous agitation. Free carbon floats to the surface and may be skimmed off. This vigorous washing step removes occluded salts, such as chloride, from the deposit, and also converts any calcium metal or calcium carbide which may be present to calcium hydroxide. An acid not attacking the titanium but solubilizing the calcium hydroxide is then added to ICC the wash water to a pH of 4.5 to 5.0. Such acid thus is not. a strong mineral acid, but a weak organic acid, as formic, acetic, citric, and the like. The metal particles are then allowed to settle to the bottom of the container and the supernatent liquid is decanted ofi. This supernatent liquid carries finely divided titanium carbide in suspension and the most of this extremely fine titanium carbide may be removed by decanting two or three times. The residual titanium metal is then filtered and ground wet to 60 to 80 mesh in order to free any occluded impurities, and the washing cycle described above including formic acid treatment is repeated. This final treatment removes all traces of calcium chloride; calcium hydroxide, calcium oxide, calcium metal, and calcium carbide. In general, such a procedure is effective ir1 providing commercially pure titanium metal suitable for direct melting, where the initial electrolytic processing has been carried out properly. However, if electrolytic processing is such that any undue amount of titanium carbide or titanium monoxide remains with the deposited metal, then it is necessary to examine the material analytically to determine the extent of the carbide and oxide contents. If titanium monoxide is present at all, that is in amounts greater than a few hundredths of a percent or if carbide is present to the extent of 1% or more, then further separation is necessary.

In order to accompilsh this separation, the powdered metal is ground in a stainless steel ball mill in water to approximately -325 mesh and the slurry which is obtained is again treated with water and formic acid washes as before to provide insurance of as complete a calcium and carbon removal as possible. The residue which is obtained is filtered and is then dried in a vacuum. Then any residual titanium monoxide or titanium carbide may be separated by a further step.

A usual type froth flotation cell (for example the Fagergren cell) is suitable. The oxide and carbide separation steps are handled consecutively. In the case of oxide or carbide, the concentration of starting power may be between 10 and 20% by weight of the total solution. With traces of calcium salts present, if it be attempted to apply flotation procedures to such a system, all of the ingredients float out of the cell without any separation. Fundamentally, it appears that this is due to the occlusion of the particles without regard to composition, such occlusion being made effective by the multivalent ion Ca2+. I have found that agents capable of msolubilizing or de-ionizing or sequestering calcium obviate this, and by thus conditioning the material, make possible the desired separation, the detrimental components being floated off, while the titanium metal remains, being in effect depressed. Especially desirable are watersoluble phosphates and glasses of the pyro-metaphosphate system. Also sulphonated fatty alcohols, their esters, and their derivatives. Frothing agents from the class of higher alcohols may also be used. The alkali metal salts of the xanthic acids are most useful as collecting agents. The crude titanium powder is dispersed in a 0.5 to 1% solution of, for example, tetrasodium pyrophosphate, and a collecting agent such as potassium ethyl xanthate in ethyl chlor-carbonate is added to the extent of 2 /2 mililiters per liter of solution. The mixture is then conditioned in the cell for 10 to 15 minutes and flotation is initiated. Titanium monoxide concentrates in the froth. Usually 2 to 3 passes are suflicient to remove all titanium monoxide present to the extent that ,it may be encountered in electrolytic titanium. (It should again be pointed out that if the conditions of the electrolysis are sufficiently good the titanium monoxide step such as just described is not necessary.)

If any amount of carbide in the form of titanium carbide is present in the deposit of titanium metal, this is removed by a flotation step. For this separation, again the concentration of crude titanium metal powder may be of the order of 10 to 20 parts by weight in the frothing solution and the solution consists primarily of a 12 to 15% solution of a complex water soluble phosphate sequestering agent, e. g., tetrasodium pyrophosphate decahydrate. Again in this case, the titanium metal is depressed and the titanium carbide floats.

After conditioning for several minutes, the carbide is allowed to float oif. It is important to note that separate flbfli efs fibl required 'Siiiii' iii this 'CO'fib'iitiititifi', tetrasodium pyrophosphate is in itself a suflicient frother in view of its detergent pro pergties. Under normal condi; tions,.the ti'tgihi'uin, carbide may be separated "ompletely in 3 .to 4 passes, but the f ro'c'ess may be facilitated by use of acid media at til-I of the order of 2.0 to 2.5. The acid used should besu'chas doesnot attack the titanium, as mentioned above'. Thus',.vvhile hydrofluoric acid is satisfactory to a limited extent in rubb'e'r lined tanks; it has the drawback that if the concentration be fob high, reaction occursbn the metal are efiicieney offrle'covery is correspondingly reduced. Phosphoric acidis' particularly satisfactory; and a cle'a'ri separation of titanium carbide from titanium metal may bebbtaiiie'd iii the presence of this agentiii one to two passes. Both in the case of the titanium monoxide ahd titanium carbide 'sep ara'tion,.the titanium metal is. recovered by washing and filtration, followed by vacuum drying.

Electrolytically termed titanium metal subjected to this washing and flotation procedure shows a titanium metal content. of 99.95% tita11iut'n-,,or better. I I

In order topjroduce inetal of a commercially useful nature from suchpo'w'd'er, the dry powder is pressed into pellets and fusedi'n a vacuum or in an inert atmosphere arc furnace. Such metal is malleable and fo'rgeable, because of its high purity and low oxygen content, and it may be worked by all usual methods applicable to ductile metals.

The followingexamples are illustrative:

I. I 125 grams of t'itaniur'n'metal powder containing 20% titanium. monoxide by weight was ground inwate'r to a 325 mesh powder in a stainless steel ball mill Thedispersion was diluted to a volume of '1 liter with distilled water, and 3 /2 grams of tetrasodium, pyrophosphate was added, and 2 /2 "cc. of potassium ethyl xanthate in a suitable organic solvent (such as ethyl chlor-carbonate). This was maintained at room temperature and treated in a froth flotationchamber of thejFahre'ngren type. Conditioning was aecomp'lished by fruiining the chamber at low speeds or under conditions whereair intake 'was shut otf for aperiod of about minutes. The'air intake valve was thenbPeiIed and flotation carried out for a period of about 15. minutes. oth thefresidue and the froth were again treated separa "'ly, resulting in 'a fconcentrate, a middles, and 'ar ot tails. The 'r'niddles were again treated resulting infa epressfed concentrate,fa'middles, and a froth tails. Thedepressed concentrate was. added to the various concentrates obtained in the'fore'going description and the froths also collected and combined. After washing and drying, 90 grams of metallic concentrate were obtained and 35 grams of froth concentrate. Analysis indicated that the titanium concentrate was substantially chemically pure; indicating a notation efliciency of the order of '90 7 j, whereas the materialjobtained in the froth fraction 'contains'app'roximately 70% titanium monoxide and 30%'titariium metal. V

The metal concentrate thus obtained after drying, compressing', 'and melting was malleable "and ductile- II, 125-grains of titanium met'al containing 20% by weight of titanium 'carbide was ground in water in a stainless steel ball mill to 325 mesh. The slurry was removed and diluted to l jliter with distilled water. 50 grams of tetrasodium pyrophosphate was a'dded and the slurry thus obtained'vvas treated in a Fahrengren cell. After conditioningffor 10"minute'sin the manner as described in Example I, the material was then vigorously floated for 15 minutes, resulting in a metal concentrate which remained in the'cell and a froth high in titanium carbide. The metal concentrate was retreated twice more and all of the froths were collected. Finally the froth was given a double treatment with the addition of 20 more grams of tetrasodium pyrophosphate. After combining the metal concentrates and the various froth tails, a yield of 92 grams of metal was obtained, which on compressing, fusion, and rolling was ductile, indicating the substantial absence of titanium carbide. The titanium carbide content of the froth was of the order of 76% thus showing a metal recovering at least of the order of 90%. (The pH during frothing was 10.5.)

III. Using starting agents having higher. or lower perce'nta'ges of tetrasodium 'py'rophosphate in the first roughing such as 60 grams of tetrasodium pyrophosphate per liter or 40 grams of tetrasodium pyr'ophosphat'e per liter gave results such that the yield of metal was between 80 and in a high state of purity. In these particular cases, the frothing time was considerably longer, and at least one more cycle was required to obtain such a state of purity. The initial roughing concentrate makeup of 50 grams of tetrasodium pyrophosphate per liter is somewhat critical for best results. The pH during frothing was 10.5.

IV. 125 grams of titanium metal containing 20% of titanium carbide was prepared as indicated in the foregoing, and 48 grams of tetrasodium pyrophosphate were added. Sufiicient phosphoric acid was then added to the batch so that a pH of 2.0 was reached. The material was then conditioned for about 10 minutes. The flotation time was about 15 minutes. A 'countercurrent cycle involving at most two passes was sufficient to develop a yield of 85 to metal of satisfactory commercial purity.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in the following claim or the equivalent of such befemploye'd.

I therefore particularly point out and distinctly claim as my invention:

The method of recovering titanium metal from a cathode deposit obtained by electrolytic decomposition of titanium monoxide in a fused halide salt bath which comprises removing halide salt adhering to the titanium metal deposit by washingfirst with water and then with an acidic aqueous medium, and'thereafter removing any titanium monoxide and titanium carbide admixed with the titanium metal deposit by grinding the washed deposit and by subjecting the ground deposit to froth flotation separation in the presence of a water soluble phosphate, and a collecting agent for titanium oxide, and recovering the residual metallic titanium.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Taggar't, Handbook of Mineral Dressing (c) 1945, sec. 12, page 34. (Copy in Div. 55.) 

